In recent years, tactile sensing has rapidly been expanding its presence in the fields of medical treatment, welfare, robot, virtual reality, and so forth.
In the automotive field, for example, it has been general to embed a pressure sensing element into a seat. This is aimed at prompting a passenger who gets on a vehicle and sits on the seat to fasten a seat belt. More specifically, upon sitting of the passenger on the vehicle seat, a predetermined level or larger load (weight) is applied to the pressure sensing element. Accordingly, a pressure sensor equipped with the pressure sensing element senses the presence of the passenger, and prompts him or her to fasten the seat belt.
Other expected applications of the pressure sensor include those in medical or nursing field.
More specifically, for example, the pressure sensing element embedded in a mattress of a bed is expected to monitor how the weight of a patient or aged person (also referred to as patient, etc., hereinafter) is applied when he or she lies thereon. By the monitoring, it becomes possible to discover that the patient, etc. has been lying on bed with a fixed posture for a long time. The monitoring enables a third party to know the time to appropriately change the posture of the patient, etc. lying on bed, for bedsore prevention.
It is also possible to use the pressure sensor for a walking aid of the patient, etc. More specifically, if an aged person, while waking with a waking aid, embedded with a pressure sensing element, should lose his or her balance, the pressure sensor can detect the unbalanced weight of the aged person as a change in pressure distribution. It is therefore expected to provide falling prevention for the aged person, or detection of falling. As described above, fields where the pressure sensor may be utilized have been diversified in these years. In particular, the pressure sensor is expected to be mounted on the surface of an article other than flat surface, or to be used in a flexible mode.
There has been proposed a pressure sensing element embodied so that a support substrate having a sensor electrode, and an opposing substrate opposed therewith and having a pressure sensitive resistor, are provided while placing an insulating film in between. In these embodiments, it is important that the sensor electrode and the pressure sensitive resistor, under no load, neither contact nor short-circuit. For this reason, there has been known an embodiment in which the insulating film serves as a spacer for keeping the sensor electrode and the pressure sensitive resistor apart by a predetermined distance.
For example, Patent Literature 1 listed below describes a stacked structure of a pressure sensor in which one circuit board having a sensor electrode provided thereon, and the other circuit board having a pressure sensitive resistor formed thereon by printing, are opposed while placing a spacer sheet in between (see Table 2 in this literature). The spacer sheet is a PET film having tacky layers formed on both surfaces thereof, and on both surfaces of which, the one circuit board and the other circuit board are bonded.
A pressure sensor disclosed in Patent Literature 2 listed below is configured by a resistor board and an electrode support substrate, which are bonded while placing in between a spacer composed of an adhesion layer (see paragraph [0031] of this literature). The literature describes that the adhesion layer is an acrylic tacky film or the like.
A pressure sensor disclosed in Patent Literature 3 listed below is configured by one base film having thereon an electrode, the other base film having thereon a pressure sensitive resistor, and a spacer interposed in between (see FIG. 1 of this literature). Without load, the mutually opposed electrode and the pressure sensitive resistor are kept apart by the thickness of the spacer. The spacer is formed using a resin film, and on both surfaces of which a thermosetting resin adhesive is provided. With the aid of tackiness of the thermosetting resin adhesive, the one base film, the other base film, and the spacer are integrated.